The National Climate Assessment is the definitive statement of current and future impacts of carbon pollution on the United States. And the picture it paints is stark: Inaction will devastate much of the arable land of the nation’s breadbasket — and ruin a livable climate for most Americans.

“Americans face choices” explains the Congressionally-mandated report by 300 leading climate scientists and experts, which was reviewed by the National Academy of Sciences. We’re already seeing serious climate impacts — such as more extreme heat waves, droughts, and deluges — and additional impacts are “now unavoidable.” But just how bad future climate change is “will still largely be determined by choices society makes about emissions.”

Let’s look at some of our choices:

Note that this figure is conservative — the A2 scenario (850 parts per million of CO2 in the air) is not as bad as the business-as-usual scenario the recent U.N. climate report used. In short, if we do nothing things could well be even worse.

Even so, the heat waves in the do-nothing case are unimaginably brutal. In the A2 scenario, across most of the United States, the hottest days — those that occur only once in 20 years — will be “about 10°F to 15°F hotter” by late in the century. So those rare 105°F days will be 115° to 120°F days.

One of the most dangerous consequences of that staggering rise in heat is a drop in soil moisture — basically precipitation minus evaporation — a key indicator of drought. Places that don’t see any drop in precipitation will still see a drop in soil moisture when it is hotter because of the evaporation, the drying out of the soil in the hot sun. Even worse is that much of the Southwest is projected to see less precipitation. Combine the two, and here is another choice for America:

PROJECTED CHANGES IN SOIL MOISTURE

Average change in soil moisture in 2071–2100 compared to 1971–2000 under the strong climate action scenario (B1, left) and the keep-doing-nothing scenario (A2, right).

Which scenario should we choose? Hint: The Dust Bowl was a sustained decrease in soil moisture of only about 15%. In the A2 scenario (which, as noted, isn’t the worst case), some parts of the Southwest are, on average, permanently in a Dust Bowl. Large parts of the Southwest AND Great Plains are so close to the edge that in years with slightly less precipitation and/or slightly more heat, they will routinely be in a Dust Bowl.

Does it really seem like a good trade-off to destroy our livable climate and our food security just to avoid a cost that the world’s leading scientists and governments agree is a mere 0.06% of annual growth? But the B1 scenario will be all but closed off to us with another decade of inaction.

One reason we can be confident in the report’s projections of the future is that the same scientists warned decades ago that we would start to see increases in heatwaves, droughts and deluges by now — and we have:

The global warming of the past 50 years is primarily due to human activities, predominantly the burning of fossil fuels….

Over the last 50 years, much of the United States has seen an increase in prolonged periods of excessively high temperatures, more heavy downpours, and in some regions, more severe droughts.

The study notes, “Evidence indicates that the human influence on climate has already roughly doubled the probability of extreme heat events such as the record-breaking summer heat experienced in 2011 in Texas and Oklahoma.” At the same time, “In some regions, prolonged periods of high temperatures associated with droughts contribute to conditions that lead to larger wildfires and longer fire seasons.”

Here’s the data on precipitation:

Those of you in the Northeast who thought you’d noticed deluges becoming more intense were right. Thanks to climate change, when it rains, it pours, literally. Ironically, what this means is that even in the regions that are expected to see a drop in precipitation, more of the precipitation they do get will be in the form of deluges, which are so intense they can wash away topsoil and generally fail to alleviate droughts.

The time to act was a long time ago when we were first warned by climate scientists, but continued inaction in the face of the vindication of those scientists and even graver warnings today, is beyond immoral.